If it fails on push, presumably friction of the motor will provide braking?
If it fails, wouldn't that be the last thing you would want it to do??? You want the nosewheel to revert to.. a plain and simple nosewheel (at least when the aircraft is moving forward).
I can't imagine this system would ever be used for pushbacks. The pilot would have no idea what is going on behind/under him/her. The engineers are not going to be able to guide a pilot out (l can just imagine the engineer saying... left hand down a bit, right hand down a bit....).
The risks seem to be too great:
1) Engineer getting run over (happened recently)
2) Headset lead getting stuck under the nosewheel (=lost comms). Wireless headsets have been trialed here.. and they failed the initial tests.
At least with a tug pushback, the tug driver can see the engineer and respond
immediately.
3) Ground vehicles ignoring rotating beacons (common)
"WT Trial... cleared for powerback after Bugsmasher123 has taxied behind you... "
On some aircraft types, you are lucky to be able to see the wingtips, let alone directly behind you.
Rgds.
NSEU